Compressibility

Incompressible

Characterizes any flow for which the maximum Mach number is less than 0.3.

Subsonic Compressible

Subsonic compressible flows are flows that are compressible but contain no shocks.

In particular, the fluid velocity must be low enough so that heat generation due to viscous shearing work on the fluid is negligible. Typically, a Mach number of 0.7-0.8 is the maximum for which this is true.

If there is heat transfer, the static Temperature equation is solved. This equation neglects viscous dissipation and pressure work effects. If there is no heat transfer, the total temperature is held constant and the static temperature is determined from:

subsonic equation

Be sure to specify a value for Total Temperature for subsonic compressible flows that do not include heat transfer. This constant value of total temperature will be used in the equation shown above.

Additionally, be sure to define a material in which density varies with Equation of State.

Compressible

Compressible flows are flows that have a Mach number greater than 0.8 with or without heat transfer and shocks.

If there is heat transfer, the total Temperature equation is solved. This equation includes terms for viscous dissipation and pressure work. The static temperature is determined from the equation shown above.

For compressible flows without heat transfer, enter a value for Total Temperature.

Additionally, the density of the fluid must vary with Equation of State.

If water is chosen as the material and compressible is selected, then the water hammer problem will be solved.

For more about running Compressible Flows

Example running a Compressible analysis